The present invention relates to gas turbine engines, and in particular, to starter-generators used on gas turbine engines. Gas turbine engines typically include one or more spools that rotate to generate thrust and/or to drive accessories. Such accessories often include one or more electrical generators, fuel pumps, oil pumps, hydraulic pumps, rotor breaks, engine starters, and/or other accessories. In some gas turbine engines, the engine starter is combined with an electrical generator to form a combination starter-generator.
In gas turbine engines with a starter-generator and more than one spool, the starter-generator is often connected to and driven by the high pressure spool. That starter-generator can then be used for rotating the high pressure spool for starting the engine. If, however, that starter-generator fails, it will not be able to start the engine until it is repaired. A starter-generator can instead be connected to and driven by the low pressure spool. However, a starter-generator connected exclusively to the low pressure spool will be unable to rotate the high pressure spool for starting.